diff --git a/docs/http/cgi.md b/docs/http/cgi.md
index 8e2309db58223b754923078da640c110a5823ab1..c667fec4ef3350299a088769a65c45d1f0075534 100644
--- a/docs/http/cgi.md
+++ b/docs/http/cgi.md
@@ -29,3 +29,7 @@ Example:
 ```c
   opts.cgi_interpreter = "C:\\ruby\\ruby.exe";
 ```
+NOTE: In the CGI handler we don't use explicitly a system call waitpid() for
+reaping zombie processes. Instead, we set the SIGCHLD handler to SIG_IGN.
+It will cause zombie processes to be reaped automatically.
+CAUTION: not all OSes (e.g. QNX) reap zombies if SIGCHLD is ignored.
\ No newline at end of file